Bullet Acceleration in Vacuum: Why Does It Stop After Exit?

[rajeshmarndi]

If a bullet is fired from a gun in vacuum(assume no gravity, no resistance).

why is it that the bullet accelerates 0 to v inside the barrel but as it exit the muzzle it stop accelerating.

Isn't when the bullet exit , it exit with some force which give it a initial velocity v.

 

[Waterfox]

As combustion gases inside the barrel expand they exert a force on the bullet, as long as the force is applied the bullet accelerates. When the bullet exits the muzzle the combustion gases can escape and will disperse in the vacuum.
Because the gas can no longer exert a force on the bullet it stops accelerating and maintains a constant velocity. It does not keep some of the force that initially accelerated it.

 

[star3t]

out of the muzzle, there is no force putting on the bullet --> a = 0

 

[rajeshmarndi]

It seems a bit difficult as the last force available to the bullet as it exit, will not provide acceleration.

Because many will think that when a stone is thrown it will accelerates to some velocity and then deaccelerate.

But that's right. Thanks for the answer.

 

[PJC01]

I can explain this phenomenon using the laws of motion and the principles of projectile motion. When a bullet is fired from a gun in a vacuum, it is subject to the principle of inertia, which states that an object in motion will continue to move at a constant velocity unless acted upon by an external force. Inside the barrel of the gun, the bullet is subject to the force of the expanding gases from the gunpowder, which causes it to accelerate from 0 to its final velocity, v.

However, as the bullet exits the muzzle of the gun, it is no longer subject to this force and is now in free flight. This means that the only force acting on the bullet is the force of gravity, which is negligible in a vacuum. Without any external force to accelerate it, the bullet will continue to move at a constant velocity, hence why it stops accelerating after exiting the muzzle.

Furthermore, the initial force from the expanding gases is not enough to sustain the acceleration of the bullet for a long period of time. As the bullet travels through the air, it experiences air resistance, which acts in the opposite direction of its motion and gradually slows it down. This, combined with the bullet's own weight, eventually causes it to come to a stop.

In summary, the bullet accelerates inside the barrel due to the force of the expanding gases, but once it exits the muzzle, it is subject to the principle of inertia and experiences negligible external forces, causing it to stop accelerating.